1. Field of the Invention
The present invention relates to non-volatile memory cell technology. More particularly, the present invention relates to an isolated-nitride-region non-volatile memory cell and to fabrication methods for forming such cells.
2. The Prior Art
Non-volatile memory cells that retain data using the phenomenon of charge trapping are known. Such memory cells include metallic-nitride-oxide-semiconductor (MNOS) memory cells and silicon-oxide-nitride-oxide-silicon (SONOS) memory cells and, more recently, silicon nano-crystal memory cells.
Silicon-nano-crystal memory cells are resistant to the defects commonly seen in floating-gate memory cells, since a short between the substrate and a single nano-crystal region does not destroy the memory cell. Silicon nano-crystal memory cells suffer from a production problem in that the formation of a good quality top oxide requires an oxidation step, which tends to destroy the nano-crystals. MNOS and SONOS type memory cells have difficulty storing charge locally due to the lateral conduction of the nitride, but otherwise work in a manner similar to that of nano-crystal devices.